Heavy duty brake drums for trucks are typically made of cast iron. Brake drums are generally of a cylindrical cup shape, having a full diameter open end designed to be placed around the brake pads. A hub end is opposite the open end and is designed with a centrally located opening to receive the wheel hub therethrough. A portion of the hub end includes the wheel lug openings.
Certain problems with such cast iron brake drums include the relatively high weight necessary for proper strength together with the need for thermal performance in the form of heat dissipation from the braking due to the contact of the brake shoes with the interior braking surface of the drum.
One focus of prior art drums has been the addition of axial ribs on the outer surface of the braking section of the drum to provide better heat dissipation and thermal performance for the brake drum. Such an arrangement is shown in U.S. Pat. No. 5,826,684. Such rib addition is undesirable as it adds material and, accordingly, weight to the brake drum, as well as creating possible clearance problems for the outer surface of the brake drum as part of the truck wheel assembly itself. Further, in ordinary iron foundry practice, it requires a more complex mold to produce a drum having external ribs and, accordingly, leads to a more expensive product to cast and finish.
While it is desirable to decrease the weight of the brake drum, concern remains for the overall strength of the drum. It is desirable, accordingly, to produce a brake drum that has as light a weight as possible, but yet provides adequate strength for the heavy-duty service to which a truck brake drum is exposed. Further, it is desirable to increase the surface area of the drum in a manner to facilitate thermal performance and cooling, without unduly decreasing the strength or service life of the brake drum.
Accordingly, it is an object of the present invention to provide a lighter weight brake drum with improved thermal performance characteristics.
It is another object of the present invention to provide a lighter weight brake drum that has adequate strength to provide good service life in a heavy-duty truck application.
The present invention provides a generally cylindrical brake drum having an open end and a hub end, with a braking section extending from the open end toward the hub end. The hub end is partially closed to form a hub receiving opening in a generally flat, radially central portion of the hub end. The transition section extends from the braking section to an intersection with the hub end. The hub end flat circular section includes a plurality of wheel lug openings extending therethrough.
The drum is usually comprised of cast iron, and the brake drum itself is manufactured in a foundry casting operation. Various finishing operations are required to complete the as-cast brake drum which include a machining of the interior surface of the braking section to form a circular smooth surface to facilitate contact with the brake shoes themselves. Further, the flange edges and raised squealer balancing band are also machined.
As part of the present invention, a plurality of first-indented sections is provided on the outer surface of the braking section. Such indented sections are usually formed during the casting operation itself by appropriate corresponding protrusions on a mold. The first-indented sections extend from a location generally near the open end or near or to the squealer balancing band at the open end along the outer surface of the braking section to and, possibly, onto the transition section. The shape of such indented sections is usually quadrilateral, but can include ovals or combinations of curved and straight section intersections.
A plurality of second-indented sections appears on an outer surface of the transition section. Such second-indented sections are generally triangular in shape, but, of course, could be of an oval or quadrilateral or a combined configuration as well. It is usual to locate each of the second-indented sections between two of the first-indented sections. Again, such second-indented sections are formed in the casting operation by appropriate protrusions from the mold that, accordingly, leave an indented section or absence of material in the actual cast brake drum itself.
A plurality of third-indented sections can be present on an inside surface or an outside surface of the hub end. Such third-indented sections are usually of a generally rectangular or quadrilateral shape, with consideration of foundry practice limitations requiring fillet corners. Further, each of the third-indented sections are usually located between two of the wheel lug openings in the circular flat surface of the hub end. Such third-indented sections can be in the form of openings that extend through the hub end.